Telephone-exchange system



(No Model.)

. G. F. DURANT.

TELEPHONE EXCHANGE SYSTEM.

Patented Ot. 16, 1883.

o 01 V H H e 0 ipur'ani hi6 637.650 7* 7Z6 lo O a 4 I] II II [If i a I a UNITED- STATES PATENT OFFICE.

GEORGE F. DURANT, OF ST. LOUIS, MISSOURI.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 286,595, dated October 16, 1883.

I Application filed August 18, 1-383. (No model.)

To aZZ whom it may concern-r -Be it known that I, GEORGE F. DURANT, of St. Louis, in the county of St. Louis and State of Missouri, have invented certain Improve ments in Telephone -EXcha-nge Systems, of: which the following is a specification."

My present invention relates to an organization of electric circuits and apparatus for direct intercommunicationby means of speaking-telephones, in which a central station is connected, by means of wires radiating there-' from, to a number of substations situated at various points within thesurrounding district. The organization and arrangements of the lines and instrument-alities in the central station are such that any two sub-stations within the district may at any moments noticebe placed in direct telephonic communication with one another. My invention relates more particularly to a special arrangement of the several circuits atthe central station, whereby annunciators or other apparatus adapted to receive callsignals from sub-stations may be entirely dispensed with; and its object is to provide a simple and efficient system of circuit construction, whereby a single listener placed at the central station can keep watch over a largenumber of lines connecting with such a station.

It consists, in a general way, in dispensing with a main central-office ground-wire, in

grouping a suitable number of lines together, and in looping a receiving-telephone or receiving and transmitting telephones between each pair of groups, so that, as hereinafter more particularly described, a large proportion 'of the articulating electrical undulations produced by speaking in the transmitter at any of the substations must necessarily p: ss through the receiver at the central oiiice which is com; mon to that group.

Heretofore, and prior to this invention, several methods for effecting. communication between the various sub-stations whose lines converge to the central station have been adopted. As a recognition of the prior state of the art I will here briefly describe them. By the first method a bell or enunciator is placed in the circuit of each converging line at the central station, and any subscriber desirous of being put into communication with any other subscriber is required to give a signal by transmitting an electrical pulsation and actuating the said bell or drop, whereupon the attending operator connects a telephone to the line of I the subscriber signaling and takes his order.

The desired sub-station is then signaled, and electrical connection between the two is eflected, in the usual manner, by means of aswitohboard. The second method, while avoiding the use of the annunciator or signal-bell at the cen' tral station, involves an additional or signal wire extending from the central offi cc to a number of the sub-stations with which the telephones of the subscriber may be connected, and which, at the central station, is connected with a receiving-telephone, at which an opermon ground-wire at the central station, and

inserts the operators receiving and transmitting telephones in the circuit of the said common ground-wire, as shown and described in Letters Patent granted to Geo. B. Scott, February 7, 1882, No. 253,316. In this system it was found necessary to insert resistances in each of the converging circuits, so as to prevent the greater part of the electrical current from being diverted from the central-office ground terminal and the telephones included therein into the remaining circuits of the converging series. Each of the methods thus described have disadvantages which I aim to overcome. The first method involves a large amount of expensive and complicated signaling apparatus, and is not so economical in the element of time as is desirable. The second is objectionable from the necessity of the additional wire, which, besides adding greatly to the cost of construction, is open to the serious objection that it makes the telephonic facilities of a great number of substations dependent upon the good order and efficiency of a single Wire inasmuch as, if the signal-wire is the central station, 0 0, after passing through terminal stations, where they are each united to a ground-wire, to a central station, 0 O,

in any way disabled, the sub-stations connected I therewith have no means of communicating with the central station.

In the drawings which accompany and form a part of this specification, Figure 1 is a diagram representing the third method, hereinbefore described, and upon which, more than any other, my present invention is an improvement. Fig. 2 is asimilar diagram, represent ing the eircuit-conneetions utilized in my invention. Fig. 3 is also a diagram illustrating the invention, in which the instrument-connections at the central and sub stations are more fully elaborated.

. In Fig. 1 the several subscribers lines 1, 2, 3, 4, 5, and 6 are shown as converging from their where they are all normally united to the metal bar a, the saidbar,furthermore,being connected by a wire, 9, through a receiving-telephone, T, and transmitter T to the ground. The object of so placing the eentral-oflice telephones in the common ground-wire is to enable the listening operator there to hear any words uttered at any of the sub-stations of the group. Experience has, however, demonstrated that when the several linecircuits are grouped in this way only a small proportion of the electrical currents pass through the central-ofiice telephone to earth, the greater part dividing itself between the remaining line-circuits in direct proportion to their respective conductivities, the telephonic articulationsin the central oflice instruments being thus rendered very faint and indistinct. To remedy this it has been proposed to insert resistances in each of the several line-circuits, so that a lessproportion of the telephonic currents will be diverted over them, a greater proportion thus taking the route through the central-office instrument, causing a corresponding increase in the loudness of the speech reproduced therein. By my invention, however, a much more satisfactory result is obtained, and the resistances may, moreover, be dispensed with. Its principle is exemplified in the diagram Fig. 2. Two groups of lines, each constituted of as many lines as may be desirable, areattached at the central station, respectively, to the conducting-bars a andc, which form the terminals of a conducting-loop, Z Z, the said loop including the transmitter T and receiver T, the former being energized in the usual manner by the battery 13. The lines radiating from one or more way-stations, s, ultimately terminate in an earth-wire at the terminal stations 1 2 3 4 5 6, and so on. By this arrangement a much greater portion of a working-current generated at any of the sub-stations passes through the central-office instruments, whereby the speech transmitted at any of the waystations is reproduced with much greater loudness and distinctness than in the method delineated in Fig. 1.

and ordinarily this would be done.

It is well known that any electrical current having a choice of routes divides'at the point of junction, the amount passing over each being directly proportionate to its relative conductivity, or inversely proportionate to its rel ative resistance. Therefore words spoken to the transmitter at any of the sub-stations on any of the lines (for example, line No. 1) will generate currents which, reaching the central station, will divide, a portion thereof being diverted through the other lines, 2, 3, 4, 5, and

'6, 011 the same side of the central-office telephones, while the remaining portion, after passing as a whole through the telephones T T at the central station, divides between the lines 7, 8, 9, 10, 11, and 12 on the other side of the said telephones. Abutton-switch, a, is provided, by which, if desired, the resistance of the transmitter T may be short-circuited, In many cases it is not necessary to hold conversation with the subscriber, and in such cases the transmitter T may be dispensed with altogether, the receiver being then the only instrument included in the loop between the two groups of circuits.

Fig. 3 shows vention in a practical form.

one way of embodying my in In it 1, 2, 5, and

7 represent the line-circuits on one side of the central-office telephones, and 3, 4, 6, and 8 an equal number of lines on the other side. These numbers are also assigned to the terminal stations of the several lines, the intermediate or way stations being designated by the letter 8. Each of the lines is grounded at G- at the terminal station. Entering the central office C O, the several lines connect with the switchboard S, which may be of any desired character. \Vhen the form shown in the drawings is used, half of the lines are, as shown, united by metal plugs 19 with the metal bar d,'and the remainder with the corresponding bar, 6. A wire, Z, fastened to the bar (I, leads to the re ceiving-telephoneT, passes thence to the transmitter T, and from thence continues to the bar 6, to which it is united. A metallic loop containing' the receiving and transmitting telephones, or, if preferred, the former only, is thus formed, of which the bars d and e are the terminals. The lowest switch-board cross-bar, z, is attached to a wire, w, leading to a springkey, K, capable of being depresscd,-andalso capable of being moved horizontally round the pivot 1*. By its own resiliency the key presses upwardagainst the bridge or back contact h, and a wire is led from thence through receiving and transmitting telephones t t to the ground; YVhen the key K is turned on its pivot to the right, it may be depressed upon by wire to a pole-changer, I, the said pole= changer also connecting with the ground by the wire 11/, and with the battery M B by the wires y and y. By connecting any of the sub- IIO scribers lines with the switch-bar 2, when the I is obvious that my invention is not dependent key is undepressed, any conversation passing on that line may be heard by the telephone L T, and, under the same conditions, whenthe key is depressed and makes contact with the right-hand button at, call-signals due to currents generated by the magneto-machine G may be sent to line. If the key is depressed onto the left-hand buttonf, battery-currents constantly reversed by the pole-changer are sent to line. It is not necessary that both of these forms of signaling apparatus shall be used; but it is convenient to have them, in order that one can be used during any temporary disablement of the other. As in Fig. 2, the transmitter T may be short-circuited by the buttonswitch a. In Fig.3 the lines 7 and 8 are carried out to show the sub-station apparatus at the stations '7 and 8. The said lines are represented as being connected with one another through the central-office switch-board.

r and transmitter T, to the ground.

The line entering the sub-station is attached, first, to the hook-switch H, and while the lines are in use continues thence by the contact point or spring 0, wire 0, receiver T, wire 0 hen the lines are not in use, the receiver hangs on the hook, and the line is thus directed, by the contact of thehook-lever with the point 0", through the signal-bell M, to the ground. B represents the transmitter-battery.

In the operation of this system it is supposed that an operator at the central station is constantly listening for orders at the operators telephone, which is normally connected with both groups of lines. Suppose, now, station 7 desires to speak with station 8. The operation is as follows: 7 removes his telephone from the hook and at once speaks to the central station, stating his desire. The operator, listening at telephone T, hears the order and removes the plug of S from its regular hole, in-

serting it at the same time into a hole on the finished, an additional plug may be placedin.

the hole at the intersection of the line-bar with the cross-bar 2, thus attaching a ground branch to the united lines. By now listening at the test-telephone t, the state of the conversation may be ascertained or, in a manner well understood, I may insert aringing-off annunciator in the circuit of two connected lines, which shall be adapted to give a disconnectingsignal upon the discontinuance of conversation, the said signal being sentby one of the two sub-stations concerned.

I do not confine myself to any specific form of switch-board or signaling device, since it upon the form of apparatus employed, Moreover, although I have shown and described but one pair of groups of sub-station lines connected with one another through the central-oflice telephones, it is evident that I do not limit myself to that or any other number, since any number of pairs of groups may be arranged in a single central station without departing from the spirit of my invention. In the arrangement which I have described I prefer to connect the same number of line-circuits with each group of a pair, as the resultant effect is thereby improved. Such a constructionis not absolutely necessary, and one or more circuits, as occasion may demand, may be taken from or added to either group without material disadvantage.

I claim 1. The combination, in a tclephoneexchange system, of one or more pairs of groups of telephone-line circuits, the lines of each group converging to a single central-ofiice terminal, with a receiving and transmitting telephone connected between the two groups of each pair, substantially as hereinbefore described.

2. In atelephonc-exchange system, the combination, substantially as hereinbefore described, of a pair of groups of telephone-line circuits, each of the said circuits converging from one or more sub-stations to a central station, a common conducting-terminal for each group of lines, and a conducting-loop including the central-station telephone or telephones, uniting the terminal of one group with the terminal of the other, whereby each of the linecircuits of both groups of a pair has a normal ground-terminal at the distant end of each of the other lines.

3. In a telephone-exchange system, apair of groups of substation telephone-lines, all the lines of both groups converging at the central station, a terminal wire for each group at the central station, to which all the line-wires of each group are united, a conductingdoop including a receiving and transmitting telephone, and constituting a connecting-link whereby the terminal of one of the groups is united with the terminal of the other group, and a short-circuiting switch adapted to shunt the transmittingtelephone, all in combination, substantially as specified.

4. The combination, in a telephone-exchange system, of a pair of groups of line-circuits, each group concentrating into a single terminal at the central station, the terminals ofthe two groups being united together to form the pair, a receiving and transmitting telephone includedin the circuit of the said united ter- IIO minals, and means for disconnecting any of the central station, with a series or telephone-line circuits connected with and radiating from one of the terminals of the said loop, and with a second series of line-circuits similarly connected with and radiating from the other terminal of the said loop, so that the joint resistance of the circuits on one side is approximately equal to that of the circuits on the other side,whereby a large proportion of the electrical undulations produced in any of the sub-station transmitters is caused to pass through the central-station instruments, substantially as and for the purposes described.

6. The combination, substantially as here inbefore described, of a pair of groups of line circuits, each group concentrating into a single terminal at the central station, the termi nals of the two groups being united together to form the pair, a receiving and transmitting telephone included in the circuit of the said united terminals, means, as indicated, for disconnecting any of the several line-circuits from the common united terminal, and for connecting I GEO. F. DURANT. \Vitnesses:

G. A. Morin, O. H. BURTON. 

